Add a test for PlainYearMonth#toPlainDate().

test/built-ins/Temporal/PlainYearMonth/prototype/toPlainDate/limits.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.toplaindate
+description: Throws a RangeError if the resulting PlainDate is out of range
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const min = Temporal.PlainYearMonth.from("-271821-04");
+assert.throws(RangeError, () => min.toPlainDate({ day: 18 }), "min");
+TemporalHelpers.assertPlainDate(min.toPlainDate({ day: 19 }),
+  -271821, 4, "M04", 19, "min");
+
+const max = Temporal.PlainYearMonth.from("+275760-09");
+assert.throws(RangeError, () => max.toPlainDate({ day: 14 }), "max");
+TemporalHelpers.assertPlainDate(max.toPlainDate({ day: 13 }),
+  275760, 9, "M09", 13, "max");